This invention relates to a method and apparatus for cell culture and more particularly to a static cell culture maintenance system.
The culture of animal cells in vitro for the production of various proteins, peptides, hormones, growth factors and other biologically active substances has been widely investigated. A great many animal cells have been utilized in cell culture to secrete important biomolecules which are of significant biomedical interest. For example, pituitary cells have been cultured in vitro to produce growth hormone; kidney cells have been cultured to produce plasminogen activator; and hepatitis-A antigen has been produced in cultured liver cells. Other cells have been specifically cultured to produce various viral vaccines and antibodies. So also, interferon, insulin, angiogenic factor, fibronectin and numerous other biomolecules have been produced by the in vitro culture of various animal cells.
A great diversity of procedures and apparatus for in vitro cell culture production of biomolecules of interest has been utilized heretofore. In certain relatively simple systems, the cells are grown to confluence in tissue flasks and roller bottles in the presence of suitable nutrient media. More complex systems have utilized capillary hollow fiber membranes as the surface support and as the means of supplying nutrient media to the cells. In the latter systems, nutrient culture media can be pumped through the lumen of hollow fibers arranged in an elongated bundle as described in U.S. Pat. Nos. 3,821,087; 4,220,725; and 4,184,922; or oxygen can be supplied through the hollow fiber membranes to maintain aerobic conditions as disclosed in U.S. Pat. No. 3,997,396.
A further improvement of the hollow fiber membrane cell culture technology employs a flat bed configuration in which the nutrient medium is supplied transverse to the bed of fibers in a relatively short flow path as seen from U.S. Pat. Nos. 4,087,327 and 4,201,845. The flat bed configuration reduces the undesirable nutrient gradient produced by the elongated cartridge or bundle configuration of the hollow fiber membranes.
Other cell culture systems propagate the cells in agitated liquid suspension culture, particularly for larger scale operations as described, for example, in U.S. Pat. Nos. 4,059,485; 4,166,768; 4,178,209; and 4,184,916. In the case of cells which require surface support, microcarriers have been employed in the suspension culture medium as the support means. Such microcarriers are illustrated, for example, in U.S. Pat. Nos. 3,717,551; 4,036,693; 4,189,534; 4,203,801; 4,237,033; 4,237,218; 4,266,032; 4,289,854; 4,293,654; and 4,335,215.
Further background information on conventional culture conditions for the production of animal cells in microcarrier culture can be had by reference to the recent paper by Clark and Hirtenstein, Ann. N.Y. Acad. Sci. 369, 33-45 (1981).
In most of the aforesaid in vitro cell culture systems, emphasis has been placed on means to stimulate proliferation of large numbers of cells or for investigation of differentiated function of very few non-proliferating cells. Although some secreted biomolecules can be produced during periods of high proliferation, more efficient production of such export biomolecules can be obtained in arrested, more differentiated states. Moreover, some in vivo secretory cells have very low proliferation rates. Accordingly, an in vitro cell culture system which allows a large number of cells to be maintained in a state of low proliferation but with continuous product secretion would be of significant value.